1. Field of the Invention
The present invention relates in general to a cathode ray tube and a manufacturing method of a deflection coil, more particularly, a cathode ray tube and a manufacturing method of a deflection coil including a deflection yoke having an opening formed on a flange section of an opening portion on a screen side of the deflection coil.
2. Discussion of the Background Art
FIG. 1 illustrates the structure of a related art cathode ray tube.
As depicted in FIG. 1, the color cathode ray tube includes a panel 1 and a funnel 2 connected to the panel 1, thereby maintaining inside thereof in vacuum state.
Inside the panel 1 is a fluorescent screen 3 containing R, G, and B fluorescent substances (or phosphors), and an electron gun 4 for emitting red, green and blue electron beams 7 is housed in a neck portion of the funnel 2 on the opposite side of the screen 3.
A shadow mask 5 for selecting colors is disposed at a predetermined position between the fluorescent screen 3 and the electron gun 4, more specifically, closer to the fluorescent screen 3, and there is an inner shield 6 made of magnetic material to reduce the movement of electron beams due to a magnetic field.
On the other hand, a convergence purity magnet (CPM) 8 and a deflection yoke 9 are mounted on the neck portion of the funnel 2. The CPM located on the side of the electron gun rearward of the deflection yoke 9 adjusts R, G, and B electron beams emitted from the electron gun 4 to converge on a point, and the deflection yoke 9 deflects the electron beams 7.
Also, a reinforcing band 10 is clamped to an outside skirt portion of the panel to reinforce the front surface glass under the influence of high vacuum state of the inside. Because the high vacuum tube is easily exploded by the external shocks, it is necessary to design the panel to be strong enough to withstand atmospheric pressure. For instance, the reinforcing band 10 on the outside skirt portion of the panel 1 distributes tension or stress acting on the high vacuum tube and thus, improves shock (or impacts) resistance of the cathode ray tube.
To briefly explain the operation of the color cathode ray tube with the above structure, the electron beams 7 emitted from the electron gun 4 are deflected vertically and horizontally by the deflection yoke 9, and the deflected electron beams 7 pass through beam passing holes on the shadow mask 5, and strike the fluorescent screen 3 on the front, consequently displaying desired color images.
FIG. 2 illustrates a more detailed structure of a deflection yoke.
Referring to FIG. 2, the deflection yoke 9 includes a horizontal deflection coil 21 for deflecting electron beams in the horizontal direction, and a vertical deflection coil 22 for deflecting electron beams in the vertical direction, a ferrite core 24 for minimizing a loss in a magnetic force generated by the horizontal and vertical deflection coils 21 and 22 on its return path, and a holder 23 for insulating between the horizontal and vertical deflection coils 21 and 22.
Generally, a horizontally deflected current having a frequency of 15.75 kHz or above travels in the horizontal deflection coil 21, and using a magnetic field generated around the coil, the deflection yoke deflects the electron beams 7 inside the cathode ray tube in the horizontal direction.
In like manner, a vertically deflected current having a frequency of 60 Hz travels in the vertical deflection coil 22, and using the magnetic field generated around the coil, the deflection yoke deflects the electron beams 7 inside the cathode ray tube in the vertical direction.
Therefore, an image gets displayed on the screen as the deflection yoke 9 deflects the electron beams 7 in the horizontal and vertical directions and converges them to a point on the screen.
One of currently developed deflection yokes is a self-convergence type deflection yoke, which uses non-uniform magnetic fields generated by the horizontal and vertical deflection coils 21 and 22, in order to converge R, G and B electron beams 7 on the screen without the help of a separate additional circuit or device.
In other words, by adjusting the turning distribution of the horizontal and vertical deflection coils 21 and 22, the self-convergence type deflection yoke creates a barrel or pin-cushion shaped magnetic field for each section (i.e., opening portion, middle portion, neck portion), and allows each of those three electron beams 7 to experience a different deflection force depending on their positions (yet to be converged upon one point despite different distances between the starting point to the arriving point on the screen), thereby striking a corresponding fluorescent screen more accurately.
Here, the opening portion on the screen side indicates a portion adjacent to the screen having a relatively greater diameter cross-section, and the opening portion on the neck side indicates a portion having a relatively less diameter cross-section on the opposite side of the screen side.
The middle portion, as the name implies, indicates a middle portion of the opening portion on the screen side and the neck portion on the neck side.
On the other hand, one of typical problems cathode ray tube manufacturers are faced with is that it is actually very difficult to deflect the electron beams 7 onto the full screen if they use only the magnetic fields generated around the horizontal and vertical deflection coils 21 and 22 by flowing the horizontally and vertically deflected currents into the coils. Hence, the ferrite core 24 with a high magnetic permeability is usually employed to minimize the loss in the magnetic fields generated by the horizontal and vertical deflections coils 21 and 22 on a return path of the magnetic fields, and further to improve a magnetic efficiency and magnetic force.
FIG. 3 illustrates a related art horizontal deflection coil.
As shown in the drawing, the horizontal deflection coil 21 is usually in a saddle shape, and using the magnetic field generated by the horizontal deflection coil 21, deflects electron beams in the horizontal direction.
However, the above horizontal deflection coil 21 alone is not sufficient to adjust an upper and lower distortions of the deflection yoke, so a correction member such as a plurality of ferrite sheets is attached to the flange portion of the opening section on the screen side to adjust the magnetic field being generated.
Moreover, to cancel a magnetic field leakage to outside, a cancel coil should be mounted at upper and lower portions of the screen side of the holder 23.